Nanoparticles are comprised of clusters of atoms with a diameter in the range of 1 to 50 nanometers. Nanoparticles have been made from metals (e.g., Pd, Cu, Fe, Ag, Ni), intermetallics (e.g., Al.sub.52 Ti.sub.48), and metal oxides (e.g., TiO.sub.2, Y.sub.2 O.sub.3, ZnO, MgO, Al.sub.2 O.sub.3).
Interest in nanoparticles has grown over the last two decades due to the unusual properties these particles possess, properties which generally arise from the large surface area to volume ratios of the particles. Once formed, the nanoparticles can be used in a powder form, used as a coating material, or condensed into nanophase materials. If denser nanophase materials are desired than achievable through cold pressing, the nanophase particles can be condensed using a hot pressing technique or sintered after the initial cold pressing step.
Nanophase materials exhibit a variety of properties. For example, nanophase metals have been reported with a yield stress and microhardness of three to five times greater than the same metals processed using conventional techniques. Nanophase ceramics exhibit vastly improved ductility and malleability. One producer of nanophase ceramics has demonstrated plastic if not superplastic deformability of a TiO.sub.2 nanophase sample by pressing a cylinder of the material into a disk. The compressed disk did not exhibit any cracks or flaws. Another advantage offered by the extremely fine grain structure of nanophase materials is their ability to achieve very uniform doping at relatively low temperatures.
Particle formation techniques include chemical and physical vapor deposition, mechanical attrition, gas phase pyrolysis and condensation, electrodeposition, cryochemical synthesis, laser pyrolysis, and gel synthesis. These techniques typically produce quantities on the order of grams per hour, quantities that are sufficient for research but generally insufficient for most commercial applications.
A technique for producing large quantities of nanoparticles, on the order of kilograms per hour, is therefore desired.